Hepatitis C virus genotype-3a core protein enhances sterol regulatory element-binding protein-1 activity through the phosphoinositide 3-kinase-Akt-2 pathway

Metabolic Dysfunction-Associated Fatty Liver Disease and Chronic Viral Hepatitis: The Interlink

Metabolic dysfunction-associated fatty liver disease (MAFLD) has now affected nearly one-third of the global population and has become the number one cause of chronic liver disease in the world because of the obesity pandemic. Chronic hepatitis resulting from hepatitis B virus (HBV) and hepatitis C virus (HCV) remain significant challenges to liver health even in the 21st century. The co-existence of MAFLD and chronic viral hepatitis can markedly alter the disease course of individual diseases and can complicate the management of each of these disorders. A thorough understanding of the pathobiological interactions between MAFLD and these two chronic viral infections is crucial for appropriately managing these patients. In this comprehensive clinical review, we discuss the various mechanisms of chronic viral hepatitis-mediated metabolic dysfunction and the impact of MAFLD on the progression of liver disease.

Hepatitis C virus induces oxidation and degradation of apolipoprotein B to enhance lipid accumulation and promote viral production

Hepatitis C virus (HCV) infection induces the degradation and decreases the secretion of apolipoprotein B (ApoB). Impaired production and secretion of ApoB-containing lipoprotein is associated with an increase in hepatic steatosis. Therefore, HCV infection-induced degradation of ApoB may contribute to hepatic steatosis and decreased lipoprotein secretion, but the mechanism of HCV infection-induced ApoB degradation has not been completely elucidated. In this study, we found that the ApoB level in HCV-infected cells was regulated by proteasome-associated degradation but not autophagic degradation. ApoB was degraded by the 20S proteasome in a ubiquitin-independent manner. HCV induced the oxidation of ApoB via oxidative stress, and oxidized ApoB was recognized by the PSMA5 and PSMA6 subunits of the 20S proteasome for degradation. Further study showed that ApoB was degraded at endoplasmic reticulum (ER)-associated lipid droplets (LDs) and that the retrotranslocation and degradation of ApoB required Derlin-1 but not gp78 or p97. Moreover, we found that knockdown of ApoB before infection increased the cellular lipid content and enhanced HCV assembly. Overexpression of ApoB-50 inhibited lipid accumulation and repressed viral assembly in HCV-infected cells. Our study reveals a novel mechanism of ApoB degradation and lipid accumulation during HCV infection and might suggest new therapeutic strategies for hepatic steatosis.

Hepatitis C virus (HCV) infection induces the degradation of apolipoprotein B (ApoB), which is the primary apolipoprotein in low-density lipoprotein (LDL) and very low-density lipoprotein (VLDL). Impaired production and secretion of ApoB-containing lipoprotein is associated with an increase in hepatic steatosis. Thus, ApoB degradation might contribute to HCV infection-induced fatty liver. Here, we found that ApoB was not degraded through endoplasmic reticulum-associated degradation (ERAD) or autophagy, as reported previously. Instead, HCV infection induced ApoB oxidation through oxidative stress, and oxidatively damaged ApoB could be recognized and directly degraded by the 20S proteasome. We also found that ApoB was retrotranslocated from the endoplasmic reticulum (ER) to lipid droplets (LDs) for degradation. Through overexpression of ApoB-50, which can mediate the assembly and secretion of LDL and VLDL, we confirmed that ApoB degradation contributed to hepatocellular lipid accumulation induced by HCV infection. Additionally, expression of ApoB-50 impaired HCV production due to the observed decrease in lipid accumulation. In this study, we identified new mechanisms of ApoB degradation and HCV-induced lipid accumulation, and our findings might facilitate the development of novel therapeutic strategies for HCV infection-induced fatty liver.

Host metabolic reprogramming in response to SARS-CoV-2 infection: A systems biology approach

Understanding the pathogenesis of SARS-CoV-2 is essential for developing effective treatment strategies. Viruses hijack the host metabolism to redirect the resources for their replication and survival. The influence of SARS-CoV-2 on host metabolism is yet to be fully understood. In this study, we analyzed the transcriptomic data obtained from different human respiratory cell lines and patient samples (nasopharyngeal swab, peripheral blood mononuclear cells, lung biopsy, bronchoalveolar lavage fluid) to understand metabolic alterations in response to SARS-CoV-2 infection. We explored the expression pattern of metabolic genes in the comprehensive genome-scale network model of human metabolism, Recon3D, to extract key metabolic genes, pathways, and reporter metabolites under each SARS-CoV-2-infected condition. A SARS-CoV-2 core metabolic interactome was constructed for network-based drug repurposing. Our analysis revealed the host-dependent dysregulation of glycolysis, mitochondrial metabolism, amino acid metabolism, nucleotide metabolism, glutathione metabolism, polyamine synthesis, and lipid metabolism. We observed different pro- and antiviral metabolic changes and generated hypotheses on how the host metabolism can be targeted for reducing viral titers and immunomodulation. These findings warrant further exploration with more samples and in vitro studies to test predictions.

HCV Proteins Modulate the Host Cell miRNA Expression Contributing to Hepatitis C Pathogenesis and Hepatocellular Carcinoma Development

Simple Summary

According to the last estimate by the World Health Organization (WHO), more than 71 million individuals have chronic hepatitis C worldwide. The persistence of HCV infection leads to chronic hepatitis, which can evolve into liver cirrhosis and ultimately into hepatocellular carcinoma (HCC). Although the pathogenic mechanisms are not fully understood, it is well established that an interplay between host cell factors, including microRNAs (miRNA), and viral components exist in all the phases of the viral infection and replication. Those interactions establish a complex equilibrium between host cells and HCV and participate in multiple mechanisms characterizing hepatitis C pathogenesis. The present review aims to describe the role of HCV structural and non-structural proteins in the modulation of cellular miRNA during HCV infection and pathogenesis.

Abstract

Hepatitis C virus (HCV) genome encodes for one long polyprotein that is processed by cellular and viral proteases to generate 10 polypeptides. The viral structural proteins include the core protein, and the envelope glycoproteins E1 and E2, present at the surface of HCV particles. Non-structural (NS) proteins consist of NS1, NS2, NS3, NS4A, NS4B, NS5a, and NS5b and have a variable function in HCV RNA replication and particle assembly. Recent findings evidenced the capacity of HCV virus to modulate host cell factors to create a favorable environment for replication. Indeed, increasing evidence has indicated that the presence of HCV is significantly associated with aberrant miRNA expression in host cells, and HCV structural and non-structural proteins may be responsible for these alterations. In this review, we summarize the recent findings on the role of HCV structural and non-structural proteins in the modulation of host cell miRNAs, with a focus on the molecular mechanisms responsible for the cell re-programming involved in viral replication, immune system escape, as well as the oncogenic process. In this regard, structural and non-structural proteins have been shown to modulate the expression of several onco-miRNAs or tumor suppressor miRNAs.

Genotype 3-hepatitis C virus’ last line of defense

Chronic infection with hepatitis C virus (HCV) is one of the leading causes of liver disease globally, affecting approximately 71 million people. The majority of them are infected with genotype (GT) 1 but infections with GT3 are second in frequency. For many years, GT3 was considered to be less pathogenic compared to other GTs in the HCV family due to its favorable response to interferon (IFN)-based regimen. However, the growing evidence of a higher rate of steatosis, more rapid progression of liver fibrosis, and lower efficacy of antiviral treatment compared to infection with other HCV GTs has changed this conviction. This review presents the specifics of the course of GT3 infection and the development of therapeutic options for GT3-infected patients in the era of direct-acting antivirals (DAA). The way from a standard of care therapy with pegylated IFN-alpha (pegIFNα) and ribavirin (RBV) through a triple combination of pegIFNα + RBV and DAA to the highly potent IFN-free pangenotypic DAA regimens is discussed along with some treatment options which appeared to be dead ends. Although the implementation of highly effective pangenotypic regimens is the most recent stage of revolution in the treatment of GT3 infection, there is still room for improvement, especially in patients with liver cirrhosis and those who fail to respond to DAA therapies, particularly those containing inhibitors of HCV nonstructural protein 5A.

Integrated Analysis of microRNA-mRNA Expression in Mouse Lungs Infected With H7N9 Influenza Virus: A Direct Comparison of Host-Adapting PB2 Mutants

MicroRNAs (miRNAs) are important regulators involved in the antiviral response to influenza virus infection, however, an analytical comparison of miRNA and mRNA expression changes induced by several H7N9 host-adapting PB2 mutants remains undone. Here, miRNA microarray and transcriptome sequencing of BALB/c mouse lungs infected with A/Anhui/1/2013 (H7N9) [hereafter referred to as H7N9/AH1-PB2-627K(WT)] and mutant variants with PB2 amino acid substitutions (avian-like H7N9/AH1-PB2-627E and mammalian-adapted H7N9/AH1-PB2-627E/701N) were directly compared. The results showed that influenza virus infection induced dysregulation of numerous host cell processes. In a miRNA-mRNA network associated with immunity, changes in the expression of 38 miRNAs and 58 mRNAs were detected following influenza virus infection. Notably, the miRNAs of mmu-miR-188-5p, mmu-miR-511-5p, mmu-miR-483-5p, and mmu-miR-690 were specifically associated with the replication of the avian-like virus H7N9/AH1-PB2-627E. Likewise, the miRNAs of mmu-miR-691, mmu-miR-329-3p, and mmu-miR-144-3p were specifically associated with the mammalian-adapted virus H7N9/AH1-PB2-627E/701N. Finally, the miRNAs of mmu-miR-98-5p, mmu-miR-103-3p, mmu-miR-199a-5p, and mmu-miR-378a-3p were specifically associated with H7N9/AH1-PB2-627K(WT) virus replication. This is the first report of comparative integration analysis of miRNA-mRNA expression of these three H7N9 influenza viruses with different host-adapting PB2 mutations. Our results highlight potential miRNAs of importance in influenza virus pathogenesis.

Effects of diet supplementation with rumen-protected betaine on carcass characteristics and fat deposition in growing lambs

This study evaluated the effects of dietary rumen-protected betaine (RPB) supplementation on the fat deposition of lambs. Sixty Hu sheep were randomly divided into 5 groups. The lambs were fed a control diet (CON) or diets supplemented with 1.1 g/d unprotected betaine (UPB), 1.1 g/d RPB, 2.2 g/d RPB or 3.3 g/d RPB for 70 days. Compared with UPB, the abdominal fat in 2.2 g/d RPB supplemented group was decreased (P < .05). Compared with CON and UPB, the fat contents in longissimus dorsi (LD) of RPB treatments were increased (P < .01). With increasing of RPB levels, the fat content in the LD was quadratically increased (P < .05). Compared with CON, genes expression of PI3K, mTOR and S6K1 in the LD of RPB treatments were up-regulated (P < .05). In conclusion, RPB supplementation decreased the abdominal fat in lambs but increased the fat content in lamb meat, and this effect might be regulated by mTOR signaling.

Hepatitis C virus nonstructural protein 5A perturbs lipid metabolism by modulating AMPK/SREBP-1c signaling

BACKGROUND

Steatosis is an important clinical manifestation associated with chronic hepatitis C virus (HCV) infection. AMP-activated protein kinase (AMPK), a major mediator of lipid metabolism, regulates HCV-associated hepatic steatosis, but the underlying mechanisms remain obscure. Here we investigated the mechanism of HCV nonstructural protein 5A (NS5A)-induced lipid accumulation by the AMPK/SREBP-1c pathway.

METHODS

We generated model mice by injecting recombinant lentiviral particles expressing the NS5A protein (genotype 3a) via the tail vein. The serum levels of alanine aminotransferase (ALT), free fatty acids (FFAs) and triglycerides (TG) were examined. H&E and Oil Red O staining were used to examine lipid droplets. Immunohistochemistry staining, quantitative real-time PCR and Western blotting were used to determine the expression of lipogenic genes.

RESULTS

Our results showed that the serum levels of ALT, FFAs and TG, as well as the accumulation of hepatic lipid droplets, were increased significantly in mice infected with NS5A-expressing lentiviral particles. NS5A inhibited AMPK phosphorylation and increased the expression levels of sterol regulatory element binding protein-1c (SREBP-1c), acetyl-coenzyme A carboxylase 1 (ACC1) and fatty acid synthase (FASN) in vivo and in vitro. Further investigation revealed that pharmacological activation or ectopic expression of AMPK neutralized the upregulation of SREBP-1c, ACC1 and FASN, and ameliorated hepatic lipid accumulation induced by NS5A. Ectopic expression of SREBP-1c enhanced NS5A-induced hepatic lipid accumulation, which was dramatically reversed by pharmacological activation of AMPK.

CONCLUSIONS

Collectively, we demonstrate that NS5A induces hepatic lipid accumulation via the AMPK/SREBP-1c pathway.

Transforming Growth Factor β Acts as a Regulatory Molecule for Lipogenic Pathways among Hepatitis C Virus Genotype-Specific Infections

Hepatitis C virus (HCV) infection promotes metabolic disorders, and the severity of lipogenic disease depends upon the infecting virus genotype. Here, we have examined HCV genotype 1-, 2-, or 3-specific regulation of lipid metabolism, involving transforming growth factor β (TGF-β)-regulated phospho-Akt (p-Akt) and peroxisome proliferator-activated receptor alpha (PPARα) axes. Since HCV core protein is one of the key players in metabolic regulation, we also examined its contribution in lipid metabolic pathways. The expression of regulatory molecules, TGF-β1/2, phospho-Akt (Ser473), PPARα, sterol regulatory element-binding protein 1 (SREBP-1), fatty acid synthase (FASN), hormone-sensitive lipase (HSL), and acyl dehydrogenases was analyzed in virus-infected hepatocytes. Interestingly, HCV genotype 3a exhibited much higher activation of TGF-β and p-Akt, with a concurrent decrease in PPARα expression and fatty acid oxidation. A significant and similar decrease in HSL, unlike in HCV genotype 1a, was observed with both genotypes 2a and 3a. Similar observations were made from ectopic expression of the core genomic region from each genotype. The key role of TGF-β was further verified using specific small interfering RNA (siRNA). Together, our results highlight a significant difference in TGF-β-induced activity for the HCV genotype 2a- or 3a-induced lipogenic pathway, exhibiting higher triglyceride synthesis and a decreased lipolytic mechanism. These results may help in therapeutic modalities for early treatment of HCV genotype-associated lipid metabolic disorders.IMPORTANCE Hepatic steatosis is a frequent complication associated with chronic hepatitis C virus (HCV) infection and is a key prognostic indicator for progression to fibrosis and cirrhosis. Several mechanisms are proposed for the development of steatosis, especially with HCV genotype 3a. Our observations suggest that transforming growth factor β (TGF-β) and peroxisome proliferator-activated receptor alpha (PPARα)-associated mechanistic pathways in hepatocytes infected with HCV genotype 2a and 3a differ from those in cells infected with genotype 1a. The results suggest that a targeted therapeutic approach for enhanced PPARα and lipolysis may reduce HCV genotype-associated lipid metabolic disorder in liver disease.

Role of SREBPs in Liver Diseases: A Mini-review

Sterol regulator element binding proteins (SREBPs) are a family of transcription factors involved in the biogenesis of cholesterol, fatty acids and triglycerides. They also regulate physiological functions of many organs, such as thyroid, brain, heart, pancreas and hormone synthesis. Beside the physiological effects, SREBPs participate in some pathological processes, diabetes, endoplasmic reticulum stress, atherosclerosis and chronic kidney disease associated with SREBP expression changes. In the liver, SREBPs are involved in the pathogenesis of nonalcoholic fatty liver disease, nonalcoholic steatohepatitis, hepatitis and hepatic cancer. There are several SREBP inhibitors that have potential for treating obesity, diabetes and cancer. This review assesses the recent findings about the roles of SREBPs in the physiology of organs' function and pathogenesis of liver diseases.

An important role of SREBP-1 in HBV and HCV co-replication inhibition by PTEN

HBV HCV co-infection leads to more severe liver diseases including liver cancer than mono-infections. Phosphatase and tensin homolog deleted on chromosome 10 (PTEN), a tumor suppressor, inhibits sterol regulatory element binding protein-1 (SREBP-1). In this study, we characterized the effect of the PTEN - SREBP-1 pathway on HBV HCV co-replication in a cellular model. We found that HBV and HCV can co-replicate in Huh-7 cells with no interference. Overexpression of PTEN inhibits, whereas PTEN knockdown enhances, HBV replication as well as HBV and HCV co-replication. Knocking down SREBP-1 decreases HBV replication in an HBx-dependent manner. SREBP-1 knockdown also decreases HCV replication. PTEN knockdown is concomitant with increased nuclear SREBP-1 levels. PTEN and SREBP-1 double knockdown results in intermediate levels of HBV and HCV replication in mono- and co-replication scenarios. Taken together, we demonstrated, for the first time, that the PTEN - SREBP-1 pathway can regulate HBV HCV co-replication.

Hepatitis C virus regulates proprotein convertase subtilisin/kexin type 9 promoter activity

Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a secretory serine protease mainly expressed in liver. Although PCSK9 has been shown to inhibit hepatitis C virus (HCV) entry and replication, whether HCV regulates PCSK9 transcription has not been well studied. PCSK9 promoter activity is modulated by numerous transcription factors including sterol-regulatory element binding protein (SREBP)-1a, -1c, -2, hepatocyte nuclear factor-1 (HNF-1), and forkhead box O3 (FoxO3). Since they are differently regulated by HCV, we studied the effects of these transcription factors on PCSK9 promoter activity in the context of HCV infection and replication. We demonstrated that PCSK9 promoter activity was up-regulated after HCV infection and in HCV genomic replicon cells. We also studied the effects of HCV proteins on the PCSK9 promoter activity. While HCV structural proteins core, E1, and E2 had no effect, NS2, NS3, NS3-4A, NS5A and NS5B enhanced, and p7 and NS4B decreased PCSK9 promoter activity. Furthermore, we showed that transcription factors SREBP-1c, HNF-1α and specificity protein 1 increased PCSK9 promoter activity in HCV replicon cells, whereas SREBP-1a, HNF-1β and FoxO3 had an inhibitory effect. These results demonstrated the molecular mechanisms of how HCV modulates PCSK9 promoter activity and advanced our understanding on the mutual interactions between HCV and PCSK9.

Exploring Genomic Variants Related to Residual Feed Intake in Local and Commercial Chickens by Whole Genomic Resequencing

Improving feed efficiency is a major goal in poultry production to reduce production costs and increase profitability. The genomic variants and possible molecular mechanisms responsible for residual feed intake (RFI) in chickens, however, remain poorly understood. In this study, using both local and commercial breeds, genome re-sequencing of low RFI and high RFI chickens was performed to elucidate the genomic variants underlying RFI. Results showed that 8,505,214 and 8,479,041 single nucleotide polymorphisms (SNPs) were detected in low and high RFI Beijing-You chickens, respectively; 8,352,008 and 8,372,769 SNPs were detected in low- and high-RFI Cobb chickens, respectively. Through a series of filtering processes, 3746 candidate SNPs assigned to 1137 genes in Beijing-You chickens and 575 candidate SNPs (448 genes) in Cobb chickens were found. The validation of the selected 191 SNPs showed that 46 SNPs were significantly associated with the RFI in an independent population of 779 Cobb chickens, suggesting that the method of screening associated SNPs with whole genome sequencing (WGS) strategy was reasonable. Functions annotation of RFI-related genes indicated that genes in Beijing-You were enriched in lipid and carbohydrate metabolism, as well as the phosphatase and tensin homolog (PTEN) signaling pathway. In Cobb, however, RFI-related genes were enriched in the feed behavior process and cAMP responsive element binding protein (CREB) signaling pathway. For both breeds, organismal development physiological processes were enriched. Correspondingly, NOS1, PHKG1, NEU3 and PIP5K1B were differentially expressed in Beijing-You, while CDC42, CSK, PIK3R3, CAMK4 and PLCB4 were differentially expressed in Cobb, suggesting that these might be key genes that contribute to RFI. The results of the present study identified numerous novel SNPs for RFI, which provide candidate biomarkers for use in the genetic selection for RFI. The study has improved knowledge of the genomic variants and potential biological pathways underlying RFI in chickens.

Interferons: Reprogramming the Metabolic Network against Viral Infection

Viruses exploit the host and induce drastic metabolic changes to ensure an optimal environment for replication and the production of viral progenies. In response, the host has developed diverse countermeasures to sense and limit these alterations to combat viral infection. One such host mechanism is through interferon signaling. Interferons are cytokines that enhances the transcription of hundreds of interferon-stimulated genes (ISGs) whose products are key players in the innate immune response to viral infection. In addition to their direct targeting of viral components, interferons and ISGs exert profound effects on cellular metabolism. Recent studies have started to illuminate on the specific role of interferon in rewiring cellular metabolism to activate immune cells and limit viral infection. This review reflects on our current understanding of the complex networking that occurs between the virus and host at the interface of cellular metabolism, with a focus on the ISGs in particular, cholesterol-25-hydroxylase (CH25H), spermidine/spermine acetyltransferase 1 (SAT1), indoleamine-2,3-dioxygenase (IDO1) and sterile alpha motif and histidine/aspartic acid domain-containing protein 1 (SAMHD1), which were recently discovered to modulate specific metabolic events and consequently deter viral infection.

MicroRNA-7 mediates cross-talk between metabolic signaling pathways in the liver

MicroRNAs (miRNAs) have emerged as critical regulators of cellular metabolism. To characterise miRNAs crucial to the maintenance of hepatic lipid homeostasis, we examined the overlap between the miRNA signature associated with inhibition of peroxisome proliferator activated receptor-α (PPAR-α) signaling, a pathway regulating fatty acid metabolism, and the miRNA profile associated with 25-hydroxycholesterol treatment, an oxysterol regulator of sterol regulatory element binding protein (SREBP) and liver X receptor (LXR) signaling. Using this strategy, we identified microRNA-7 (miR-7) as a PPAR-α regulated miRNA, which activates SREBP signaling and promotes hepatocellular lipid accumulation. This is mediated, in part, by suppression of the negative regulator of SREBP signaling: ERLIN2. miR-7 also regulates genes associated with PPAR signaling and sterol metabolism, including liver X receptor β (LXR-β), a transcriptional regulator of sterol synthesis, efflux, and excretion. Collectively, our findings highlight miR-7 as a novel mediator of cross-talk between PPAR, SREBP, and LXR signaling pathways in the liver.

The role of PTEN - HCV core interaction in hepatitis C virus replication

Hepatitis C virus (HCV) infection leads to severe liver diseases including hepatocellular carcinoma (HCC). Phosphatase and tensin homolog deleted on chromosome 10 (PTEN), a tumour suppressor, is frequently mutated or deleted in HCC tumors. PTEN has previously been demonstrated to inhibit HCV secretion. In this study, we determined the effects of PTEN on the other steps in HCV life cycle, including entry, translation, and replication. We showed that PTEN inhibits HCV entry through its lipid phosphatase activity. PTEN has no effect on HCV RNA translation. PTEN decreases HCV replication and the protein phosphatase activity of PTEN is essential for this function. PTEN interacts with the HCV core protein and requires R50 in domain I of HCV core and PTEN residues 1–185 for this interaction. This interaction is required for PTEN-mediated inhibition of HCV replication. This gives rise to a reduction in PTEN levels and intracellular lipid abundance, which may in turn regulate HCV replication. HCV core domain I protein increases the lipid phosphatase activity of PTEN in an in vitro assay, suggesting that HCV infection can also regulate PTEN. Taken together, our results demonstrated an important regulatory role of PTEN in the HCV life cycle.

Hepatitis C Virus-Genotype 3: Update on Current and Emergent Therapeutic Interventions

PURPOSE OF REVIEW

Direct-acting antiviral agents (DAAs) have markedly improved the prognosis of hepatitis C virus (HCV)-genotype 3 (GT3), a highly prevalent infection worldwide. However, in patients with hepatic fibrosis, cirrhosis, or hepatocellular carcinoma (HCC), GT3 infection presents a treatment challenge compared with other genotypes. The dependence of the HCV life cycle on host lipid metabolism suggests the possible utility of targeting host cellular factors for combination anti-HCV therapy. We discuss current and emergent DAA regimens for HCV-GT3 treatment. We then summarize recent research findings on the reliance of HCV entry, replication, and virion assembly on host lipid metabolism.

RECENT FINDINGS

Current HCV treatment guidelines recommend the use of daclatasvir plus sofosbuvir (DCV/SOF) or sofosbuvir plus velpatasvir (SOF/VEL) for the management of GT3 based upon clinical efficacy [≥88% overall sustained virological response (SVR)] and tolerability. Potential future DAA options, such as SOF/VEL co-formulated with GS-9857, also look promising in treating cirrhotic GT3 patients. However, HCV resistance to DAAs will likely continue to impact the therapeutic efficacy of interferon-free treatment regimens. Disruption of HCV entry by targeting required host cellular receptors shows potential in minimizing HCV resistance and broadening therapeutic options for certain subpopulations of GT3 patients. The use of cholesterol biosynthesis and transport inhibitors may also improve health outcomes for GT3 patients when used synergistically with DAAs. Due to the morbidity and mortality associated with HCV-GT3 infection compared to other genotypes, efforts should be made to address current limitations in the therapeutic prevention and management of HCV-GT3 infection.

Genotype 3 Infection: The Last Stand of Hepatitis C Virus

Hepatitis C virus (HCV) represents a significant global disease burden, with an estimated 130-150 million people worldwide living with chronic HCV infection. Within the six major clinical HCV genotypes, genotype 3 represents 22-30% of all infection and is described as a unique entity with higher rates of steatosis, faster progression to cirrhosis, and higher rates of hepatocellular carcinoma. Hepatic steatosis in the setting of hepatitis C genotype 3 (HCV-3) is driven by viral influence on three major pathways: microsomal triglyceride transfer protein, sterol regulatory element-binding protein-1c, and peroxisome proliferator-associated receptor-α. Historically with direct-acting antivirals, the rates of cure for HCV-3 therapies lagged behind the other genotypes. As current therapies for HCV-3 continue to close this gap, it is important to be cognizant of common drug interactions such as acid-suppressing medication and amiodarone. In this review, we discuss the rates of steatosis in HCV-3, the mechanisms behind HCV-3-specific steatosis, and current and future therapies.

Thioredoxin-interacting protein regulates lipid metabolism via Akt/mTOR pathway in diabetic kidney disease

Abnormal lipid metabolism contributes to the renal lipid accumulation, which is associated with diabetic kidney disease, but its precise mechanism remains unclear. The growing evidence demonstrates that thioredoxin-interacting protein is involved in regulating cellular glucose and lipid metabolism. Here, we investigated the effects of thioredoxin-interacting protein on lipid accumulation in diabetic kidney disease. In contrast to the diabetic wild-type mice, the physical and biochemical parameters were improved in the diabetic thioredoxin-interacting protein knockout mice. The increased renal lipid accumulation, expression of acetyl-CoA carboxylase, fatty acid synthase and sterol regulatory element binding protein-1, and phosphorylated Akt and mTOR associated with diabetes in wild-type mice was attenuated in diabetic thioredoxin-interacting protein knockout mice. Furthermore, thioredoxin-interacting protein knockout significantly increased the expression of peroxisome proliferator-activated receptor-α, acyl-coenzyme A oxidase 1 and carnitine palmitoyltransferaser 1 in diabetic kidneys. In vitro experiments, using HK-2 cells, revealed that knockdown of thioredoxin-interacting protein inhibited high glucose-mediated lipid accumulation, expression of acetyl-CoA carboxylase, fatty acid synthase and sterol regulatory element binding protein-1, as well as activation of Akt and mTOR. Moreover, knockdown of thioredoxin-interacting protein reversed high glucose-induced reduction of peroxisome proliferator-activated receptor-α, acyl-coenzyme A oxidase 1 and carnitine palmitoyltransferaser 1 expression in HK-2 cells. Importantly, blockade of Akt/mTOR signaling pathway with LY294002, a specific PI3K inhibitor, replicated these effects of thioredoxin-interacting protein silencing. Taken together, these data suggest that thioredoxin-interacting protein deficiency alleviates diabetic renal lipid accumulation through regulation of Akt/mTOR pathway, thioredoxin-interacting protein may be a potential therapeutic target for diabetic kidney disease.

PI3K-Akt signaling pathway upregulates hepatitis C virus RNA translation through the activation of SREBPs

Hepatitis C virus (HCV) activates PI3K-Akt signaling to enhance entry and replication. Here, we found that this pathway also increased HCV translation. Knocking down the three Akt isoforms significantly decreased, whereas ectopic expression increased HCV translation. HCV translation upregulation by Akt required their kinase activities because Akt kinase-dead mutants downregulated HCV translation; and was dependent on PI3K activity since it was sensitive to PI3K inhibitor wortmannin. The viral 3'UTR was not involved in translation upregulation by Akt. HCV NS5A increased Akt phosphorylation/activity and HCV translation in the absence of the viral 3'UTR. Sterol regulatory element-binding proteins (SREBPs) were the downstream effectors of the PI3K-Akt pathway in regulating HCV translation because Akt1 and Akt2 activated both SREBP-1 and SREBP-2, whereas Akt3 upregulated SREBP-1. Knocking down SREBPs significantly decreased, while ectopic expression of SREBPs increased HCV translation. Taken together, we showed that the PI3K-Akt signaling pathway positively regulates HCV translation through SREBPs.

Increased hepatic expression of miRNA-122 in patients infected with HCV genotype 3

Hepatitis C virus (HCV) infection affects approximately 3 % of the world population. HCV targets hepatic tissue, and most infected patients develop a chronic infection. Currently, studies have demonstrated an association between HCV-RNA replication and miR-122, the most abundant microRNA in the liver. Our aim was to evaluate liver and serum expression of miR-122 in patients infected with HCV genotypes 1 and 3, and to identify possible associations between miR-122 expression and lipid profiles, HCV viral load, apolipoproteins and liver enzymes. MicroRNAs were isolated from blood and liver tissue, and miR-122 expression was quantified by real-time PCR. HCV viral load was quantified by real-time PCR and HCV genotype, and serum biomarkers were obtained from medical report. The levels of miR-122 were higher in liver than those in blood from individuals infected with HCV genotypes 1 and 3 (p < 0.0001). The tissue levels of miR-122 were higher in subjects infected with HCV genotype 3 (6.22-fold, p < 0.001). A positive correlation was observed between the blood and hepatic levels of miR-122 in patients infected with HCV genotype 1 (r = 0.302, p = 0.026); in these patients, an inverse correlation was observed between serum apolipoprotein A-II (ApoA-II) levels and the blood (r = -0.330; p = 0.014) and hepatic (r = -0.311; p = 0.020) levels of miR-122. In patients infected with HCV genotype 3, there was a positive correlation between the hepatic miR-122 and the high-density lipoprotein-HDL (r = 0.412, p = 0.036) and insulin (r = 0.478, p = 0.044). Lipid metabolism proteins and miR-122 expression levels have different relations in HCV-3- and HCV-1-infected patients.

Associations between responses to interferon therapy and genetic variation in interleukin-28B and the core region of hepatitis C virus genotype 3a

The single-nucleotide polymorphism (SNP) of interleukin-28B (IL-28B) and mutations in the core region of hepatitis C virus (HCV) genotype 1b have been associated with response to interferon (IFN) therapy. However, whether this IL-28B SNP affects responses to INF therapy for HCV genotype 3a is not known. The aim of this study is to investigate whether this IL-28B SNP (rs8099917) and specific missense mutations in the HCV core region affect the response to IFN therapy for HCV genotype 3a. Patients (n = 19; median age 44.5) infected with HCV genotype 3a who received IFN therapy were studied. Of the 19 patients, 12 (63.1%) achieved sustained virological response. Of those 12 patients, 11 had the TT genotype (11/16; 68.7%), and one had the TG genotype (1/3; 33.3%). The difference in the sustained virological response rate between IL-28B genotype groups was not significant (P = 0.5232). HCV core region was well conserved; however, polymorphisms at position 72 were identified. Of the 19 HCV samples; 15 carried a glutamic acid at position 72, and these were defined as E type; the others (4/19) were defined as non-E type. Notably, there was a significant difference in the sustained virological response rate between E type and non-E-type; 12 of the 15 patients with E-type achieved sustained virological response, but none of the four patients with non-E-type achieved sustained virological response (P = 0.009). A glutamic acid at position 72 in the core region of HCV genotype 3a was associated with a good response to IFN therapy. J. Med. Virol. 87:1361-1367, 2015. © 2015 Wiley Periodicals, Inc.

K312 and E446 are involved in HCV RNA translation modulation by NS5A domains II and III

HCV NS5A plays a critical role in the HCV life cycle. We previously demonstrated that NS5A down-regulates viral translation through a mechanism requiring the polyU/UC region of the viral 3'UTR and that each of the three domains is capable of carrying out this function individually. In this study, we mapped the regions and amino acid residues within domains II and III involved in the modulation of viral translation. Using a series of deletion and amino acid substitution mutants, we found that K312 and E446 play important roles in the modulation of viral translation by NS5A domains II and III, respectively. In the context of full-length NS5A, mutations of K312 and E446 alone or in combination again abrogate translation down-regulation. In a transient replication assay using HCV subgenomic replicons, the K312A mutation alone does not affect HCV replication throughout a 96-h time course. While the E446A mutation can increase HCV replication at early time points (4-24 h), the K312A and E446A double mutation can enhance viral replication at 24-96 h, suggesting both residues are involved. Our results shed more light on the functions of NS5A.

The Regulation of Lipid Deposition by Insulin in Goose Liver Cells Is Mediated by the PI3K-AKT-mTOR Signaling Pathway

Background

We previously showed that the fatty liver formations observed in overfed geese are accompanied by the activation of the PI3K-Akt-mTOR pathway and an increase in plasma insulin concentrations. Recent studies have suggested a crucial role for the PI3K-Akt-mTOR pathway in regulating lipid metabolism; therefore, we hypothesized that insulin affects goose hepatocellular lipid metabolism through the PI3K-Akt-mTOR signaling pathway.

Methods

Goose primary hepatocytes were isolated and treated with serum-free media supplemented with PI3K-Akt-mTOR pathway inhibitors (LY294002, rapamycin, and NVP-BEZ235, respectively) and 50 or 150 nmol/L insulin.

Results

Insulin induced strong effects on lipid accumulation as well as the mRNA and protein levels of genes involved in lipogenesis, fatty acid oxidation, and VLDL-TG assembly and secretion in primary goose hepatocytes. The stimulatory effect of insulin on lipogenesis was significantly decreased by treatment with PI3K-Akt-mTOR inhibitors. These inhibitors also rescued the insulin-induced down-regulation of fatty acid oxidation and VLDL-TG assembly and secretion.

Conclusion

These findings suggest that the stimulatory effect of insulin on lipid deposition is mediated by PI3K-Akt-mTOR regulation of lipogenesis, fatty acid oxidation, and VLDL-TG assembly and secretion in goose hepatocytes.

Downregulation of viral RNA translation by hepatitis C virus non-structural protein NS5A requires the poly(U/UC) sequence in the 3' UTR

Hepatitis C virus (HCV) non-structural protein 5A (NS5A) is essential for viral replication; however, its effect on HCV RNA translation remains controversial partially due to the use of reporters lacking the 3' UTR, where NS5A binds to the poly(U/UC) sequence. We investigated the role of NS5A in HCV translation using a monocistronic RNA containing a Renilla luciferase gene flanked by the HCV UTRs. We found that NS5A downregulated viral RNA translation in a dose-dependent manner. This downregulation required both the 5' and 3' UTRs of HCV because substitution of either sequence with the 5' and 3' UTRs of enterovirus 71 or a cap structure at the 5' end eliminated the effects of NS5A on translation. Translation of the HCV genomic RNA was also downregulated by NS5A. The inhibition of HCV translation by NS5A required the poly(U/UC) sequence in the 3' UTR as NS5A did not affect translation when it was deleted. In addition, we showed that, whilst the amphipathic α-helix of NS5A has no effect on viral translation, the three domains of NS5A can inhibit translation independently, also dependent on the presence of the poly(U/UC) sequence in the 3' UTR. These results suggested that NS5A downregulated HCV RNA translation through a mechanism involving the poly(U/UC) sequence in the 3' UTR.

Stronger activation of SREBP-1a by nucleus-localized HBx

We previously showed that hepatitis B virus (HBV) X protein activates the sterol regulatory element-binding protein-1a (SREBP-1a). Here we examined the role of nuclear localization of HBx in this process. In comparison to the wild-type and cytoplasmic HBx, nuclear HBx had stronger effects on SREBP-1a and fatty acid synthase transcription activation, intracellular lipid accumulation and cell proliferation. Furthermore, nuclear HBx could activate HBV enhancer I/X promoter and was more effective on up-regulating HBV mRNA level in the context of HBV replication than the wild-type HBx, while the cytoplasmic HBx had no effect. Our results demonstrate the functional significance of the nucleus-localized HBx in regulating host lipogenic pathway and HBV replication.

Soraphen A: A Probe for Investigating the Role of de Novo Lipogenesis during Viral Infection

Many viruses including the hepatitis C virus (HCV) induce changes to the infected host cell metabolism that include the up-regulation of lipogenesis to create a favorable environment for the virus to propagate. The enzyme acetyl-CoA carboxylase (ACC) polymerizes to form a supramolecular complex that catalyzes the rate-limiting step of de novo lipogenesis. The small molecule natural product Soraphen A (SorA) acts as a nanomolar inhibitor of acetyl-CoA carboxylase activity through disruption of the formation of long highly active ACC polymers from less active ACC dimers. We have shown that SorA inhibits HCV replication in HCV cell culture models expressing subgenomic and full-length replicons (IC50 = 5 nM) as well as a cell culture adapted virus. Using coherent anti-Stokes Raman scattering (CARS) microscopy, we have shown that SorA lowers the total cellular lipid volume in hepatoma cells, consistent with a reduction in de novo lipogenesis. Furthermore, SorA treatment was found to depolymerize the ACC complexes into less active dimers. Taken together, our results suggest that SorA treatment reverses HCV-induced lipid accumulation and demonstrate that SorA is a valuable probe to study the roles of ACC polymerization and enzymatic activity in viral pathogenesis.

Facts and fictions of HCV and comorbidities: steatosis, diabetes mellitus, and cardiovascular diseases

The hepatitis C virus (HCV) is a major cause of chronic hepatitis, cirrhosis and hepatocellular carcinoma worldwide. A significant portion of the morbidity and mortality associated with HCV is a consequence of numerous HCV-associated comorbidities. Type 2 diabetes and atherosclerosis, two known complications of the metabolic syndrome, are noteworthy, because HCV has been suggested to play a role in their pathogenesis. In addition, HCV also causes steatosis, which may increase the risk of cardiovascular events. This review summarizes the evidence supporting the association between HCV and steatosis, insulin resistance/type 2 diabetes and cardiovascular morbidity and mortality. Their diagnostic, prognostic and management aspects are discussed.

Phosphorylation of PRAS40-Thr246 involved in renal lipid accumulation of diabetes

Lipid accumulation of kidney is a threat to renal physiological function of diabetes. The previous studies on diabetic nephropathy have demonstrated that activated Akt was involved in renal lipogenesis through enhancing transcription factor SREBP-1. PRAS40 is one of the downstream targets of activated Akt that was reported to involve in lipid metabolism in hepatic cells. However, it is still not clear whether PRAS40 is also involved in the renal lipogenesis of diabetes. Our study revealed that phosphorylation of PRAS40-Thr246 known as inactivated style increased in renal tubular cells of diabetic rats accompanied with over-expression of phospho-Akt, SREBP-1, and ADRP. In addition, in vitro experiment also found that high glucose enhanced expression of phospho-PRAS40-Thr246 followed by increased SREBP-1 and lipid droplets in HKC cells. After treated with LY294002, high glucose-induced HKC cells showed decreased phospho-PRAS40-Thr246, phospho-Akt-Ser473, and SREBP-1. Furthermore, wild type PRAS40 vector-caused increased phospho-PRAS40-Thr246 exaggerated lipid deposits in high glucose-treated HKC cells, which was effectively prevented in cells transfected with mutant PRAS40 vector (T246A). These above data suggested that phosphorylation of PRAS40-Thr246 mediated abnormal lipid metabolism in kidney of diabetes and might be the potential target for treating lipogenesis of diabetic nephropathy.

Production and pathogenicity of hepatitis C virus core gene products

Hepatitis C virus (HCV) is a major cause of chronic liver diseases, including steatosis, cirrhosis and hepatocellular carcinoma, and its infection is also associated with insulin resistance and type 2 diabetes mellitus. HCV, belonging to the Flaviviridae family, is a small enveloped virus whose positive-stranded RNA genome encoding a polyprotein. The HCV core protein is cleaved first at residue 191 by the host signal peptidase and further cleaved by the host signal peptide peptidase at about residue 177 to generate the mature core protein (a.a. 1-177) and the cleaved peptide (a.a. 178-191). Core protein could induce insulin resistance, steatosis and even hepatocellular carcinoma through various mechanisms. The peptide (a.a. 178-191) may play a role in the immune response. The polymorphism of this peptide is associated with the cellular lipid drop accumulation, contributing to steatosis development. In addition to the conventional open reading frame (ORF), in the +1 frame, an ORF overlaps with the core protein-coding sequence and encodes the alternative reading frame proteins (ARFP or core+1). ARFP/core+1/F protein could enhance hepatocyte growth and may regulate iron metabolism. In this review, we briefly summarized the current knowledge regarding the production of different core gene products and their roles in viral pathogenesis.

Are statins a viable option for the treatment of infections with the hepatitis C virus?

Statins are 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors that are widely used for the treatment of hypercholesterolemia. Besides their cholesterol-lowering effect, statins have been reported to have antiviral activity against a variety of viruses, including hepatitis C virus (HCV). Several statins inhibit the in vitro replication of subgenomic HCV replicons and also suppress in vitro RNA replication of infectious HCV. The precise mechanism of the anti-HCV activity of statins has not yet been defined. Recent studies suggest that the antiviral effect may result from the inhibition of geranylgeranylation of cellular proteins, rather than the inhibition of cholesterol synthesis. Despite the antiviral effect observed in vitro, statin monotherapy seems to be insufficient for the treatment of chronic HCV infection. However, several prospective and retrospective studies have demonstrated that the addition of statins to IFN-α and ribavirin therapy increases SVR, RVR, and EVR rates without the occurrence of additional adverse events. These clinical data, together with the excellent safety profile and low cost, suggest that statins may play a role in HCV therapy until more potent and safe direct-acting antivirals become available. This article forms part of a symposium in Antiviral Research on "Hepatitis C: next steps toward global eradication."

Hepatitis C virus induced up-regulation of microRNA-27: a novel mechanism for hepatic steatosis

MicroRNAs (miRNAs) are small RNAs that posttranscriptionally regulate gene expression. Their aberrant expression is commonly linked with diseased states, including hepatitis C virus (HCV) infection. Herein, we demonstrate that HCV replication induces the expression of miR-27 in cell culture and in vivo HCV infectious models. Overexpression of the HCV proteins core and NS4B independently activates miR-27 expression. Furthermore, we establish that miR-27 overexpression in hepatocytes results in larger and more abundant lipid droplets, as observed by coherent anti-Stokes Raman scattering (CARS) microscopy. This hepatic lipid droplet accumulation coincides with miR-27b's repression of peroxisome proliferator-activated receptor (PPAR)-α and angiopoietin-like protein 3 (ANGPTL3), known regulators of triglyceride homeostasis. We further demonstrate that treatment with a PPAR-α agonist, bezafibrate, is able to reverse the miR-27b-induced lipid accumulation in Huh7 cells. This miR-27b-mediated repression of PPAR-α signaling represents a novel mechanism of HCV-induced hepatic steatosis. This link was further demonstrated in vivo through the correlation between miR-27b expression levels and hepatic lipid accumulation in HCV-infected SCID-beige/Alb-uPa mice.

CONCLUSION

Collectively, our results highlight HCV's up-regulation of miR-27 expression as a novel mechanism contributing to the development of hepatic steatosis.

Modulation of fatty acid synthase enzyme activity and expression during hepatitis C virus replication

The hepatitis C virus (HCV) induces alterations of host cells to facilitate its life cycle. Fatty acid synthase (FASN) is a multidomain enzyme that plays a key role in the biosynthesis of fatty acids and is upregulated during HCV infection. Herein, we applied activity-based protein profiling (ABPP) that allows for the identification of differentially active enzymes in complex proteomic samples, to study the changes in activity of FASN during HCV replication. For this purpose, we used an activity-based probe based on the FASN inhibitor Orlistat, and observed an increase in the activity of FASN in the presence of a subgenomic and a genomic HCV replicon as well as in chimeric SCID/Alb-uPA mice infected with HCV genotype 1a. To study the molecular basis for this increase in FASN activity, we overexpressed individual HCV proteins in Huh7 cells and observed increased expression and activity of FASN in the presence of core and NS4B, as measured by western blots and ABPP, respectively. Triglyceride levels were also elevated in accordance with FASN expression and activity. Lastly, immunofluorescence and ABPP imaging analyses demonstrated that while the abundance and activity of FASN increases significantly in the presence of HCV, its localization does not change. Together these data suggest that the HCV-induced production of fatty acids and neutral lipids is provided by an increase in FASN abundance and activity that is sufficient to allow HCV propagation without transporting FASN to the replication complexes.

Phospho-mTOR: a novel target in regulation of renal lipid metabolism abnormality of diabetes

The activation of Akt has been proved to involve in the lipogenesis of diabetic nephropathy. However, it's still not clear whether mTOR, another main gene in PI3K/Akt pathway, is also involved in the renal lipogenesis of diabetes. In the present study, it was revealed that the phosphorylation of mTOR was up-regulated in the renal tubular cells of diabetic rats, followed by the over-expression of SREBP-1, ADRP and lipogenesis. Again, high glucose increased the expression of phospho-mTOR accompanied with SREBP-1 and ADRP up-regulation and lipid accumulation in HKC cells. Rapamycin, known as mTOR inhibitor, was used to inhibit the activation of mTOR, which prevented effectively high glucose-induced SREBP-1 up-regulation and lipogenesis in HKC cells. Furthermore, high glucose-stimulated HKC cells transfected with wild-type mTOR vector showed the enhanced SREBP-1 and lipid droplets, however, TE mTOR vector (kinase dead)-transfected HKC cells presented resistance to high glucose and decreased SREBP-1 expression and lipogenesis. These above data suggested that phospho-mTOR mediated lipid accumulation in renal tubular cells of diabetes and might be the potential targets for treating lipogenesis of diabetic nephropathy.

Fluorescence lifetime imaging of alterations to cellular metabolism by domain 2 of the hepatitis C virus core protein

Hepatitis C virus (HCV) co-opts hepatic lipid pathways to facilitate its pathogenesis. The virus alters cellular lipid biosynthesis and trafficking, and causes an accumulation of lipid droplets (LDs) that gives rise to hepatic steatosis. Little is known about how these changes are controlled at the molecular level, and how they are related to the underlying metabolic states of the infected cell. The HCV core protein has previously been shown to independently induce alterations in hepatic lipid homeostasis. Herein, we demonstrate, using coherent anti-Stokes Raman scattering (CARS) microscopy, that expression of domain 2 of the HCV core protein (D2) fused to GFP is sufficient to induce an accumulation of larger lipid droplets (LDs) in the perinuclear region. Additionally, we performed fluorescence lifetime imaging of endogenous reduced nicotinamide adenine dinucleotides [NAD(P)H], a key coenzyme in cellular metabolic processes, to monitor changes in the cofactor’s abundance and conformational state in D2-GFP transfected cells. When expressed in Huh-7 human hepatoma cells, we observed that the D2-GFP induced accumulation of LDs correlated with an increase in total NAD(P)H fluorescence and an increase in the ratio of free to bound NAD(P)H. This is consistent with an approximate 10 fold increase in cellular NAD(P)H levels. Furthermore, the lifetimes of bound and free NAD(P)H were both significantly reduced – indicating viral protein-induced alterations in the cofactors’ binding and microenvironment. Interestingly, the D2-expressing cells showed a more diffuse localization of NAD(P)H fluorescence signal, consistent with an accumulation of the co-factor outside the mitochondria. These observations suggest that HCV causes a shift of metabolic control away from the use of the coenzyme in mitochondrial electron transport and towards glycolysis, lipid biosynthesis, and building of new biomass. Overall, our findings demonstrate that HCV induced alterations in hepatic metabolism is tightly linked to alterations in NAD(P)H functional states.

Hepatitis C virus replication is modulated by the interaction of nonstructural protein NS5B and fatty acid synthase

Hepatitis C virus (HCV) nonstructural protein 5B (NS5B) is an RNA-dependent RNA polymerase (RdRp) that acts as a key player in the HCV replication complex. Understanding the interplay between the viral and cellular components of the HCV replication complex could provide new insight for prevention of the progression of HCV-associated hepatocellular carcinoma (HCC). In this study, the NS5B protein was used as the bait in a pulldown assay to screen for NS5B-interacting proteins that are present in Huh7 hepatoma cell lysates. After mass spectrophotometric analysis, fatty acid synthase (FASN) was found to interact with NS5B. Coimmunoprecipitation and double staining assays further confirmed the direct binding between NS5B and FASN. The domain of NS5B that interacts with FASN was also determined. Moreover, FASN was associated with detergent-resistant lipid rafts and colocalized with NS5B in active HCV replication complexes. In addition, overexpression of FASN enhanced HCV expression in Huh7/Rep-Feo cells, while transfection of FASN small interfering RNA (siRNA) or treatment with FASN-specific inhibitors decreased HCV replication and viral production. Notably, FASN directly increased HCV NS5B RdRp activity in vitro. These results together indicate that FASN interacts with NS5B and modulates HCV replication through a direct increase of NS5B RdRp activity. FASN may thereby serve as a target for the treatment of HCV infection and the prevention of HCV-associated HCC progression.

SREBP-1a activation by HBx and the effect on hepatitis B virus enhancer II/core promoter

Hepatitis B virus (HBV) X protein (HBx) plays an important role in HBV pathogenesis by regulating gene expression. Sterol regulatory element binding protein-1a (SREBP-1a) is a key transcriptional factor for modulating fatty acid and cholesterol synthesis. Here we demonstrated that HBx increased mature SREBP-1a protein level in the nucleus and its activity as a transcription factor. We further showed that the up-regulation of SREBP-1a by HBx occurred at the transcriptional level after ectopic expression and in the context of HBV replication. Deletional analysis using SREBP-1a promoter revealed that the sequence from -436 to -398 in the promoter was required for its activation by HBx. This promoter region possesses the binding sequences for two basic leucine zipper (b-ZIP) transcription factors, namely C/EBP and E4BP4. Mutagenesis of the binding sequences on the SREBP-1a promoter and ectopic expression experiments demonstrated that C/EBPα enhanced SREBP-1a activation by HBx, while E4BP4 had an inhibitory effect. C/EBPα was able to significantly reverse the inhibitory activity of E4BP4 on SREBP-1a promoter. These results demonstrated that HBx activates SREBP-1a activity at the transcription level through a complex mechanism involving two bZIP transcription factors C/EBP and E4BP4 with C/EBP being the dominant positive factor. Finally, we showed that knocking down SREBP-1 abolishes HBV enhancer II/core promoter activation by HBx.

Increased phosphoenolpyruvate carboxykinase gene expression and steatosis during hepatitis C virus subgenome replication: role of nonstructural component 5A and CCAAT/enhancer-binding protein β

Chronic hepatitis C virus (HCV) infection greatly increases the risk for type 2 diabetes and nonalcoholic steatohepatitis; however, the pathogenic mechanisms remain incompletely understood. Here we report gluconeogenic enzyme phosphoenolpyruvate carboxykinase (PEPCK) transcription and associated transcription factors are dramatically up-regulated in Huh.8 cells, which stably express an HCV subgenome replicon. HCV increased activation of cAMP response element-binding protein (CREB), CCAAT/enhancer-binding protein (C/EBPβ), forkhead box protein O1 (FOXO1), and peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α) and involved activation of the cAMP response element in the PEPCK promoter. Infection with dominant-negative CREB or C/EBPβ-shRNA significantly reduced or normalized PEPCK expression, with no change in PGC-1α or FOXO1 levels. Notably, expression of HCV nonstructural component NS5A in Huh7 or primary hepatocytes stimulated PEPCK gene expression and glucose output in HepG2 cells, whereas a deletion in NS5A reduced PEPCK expression and lowered cellular lipids but was without effect on insulin resistance, as demonstrated by the inability of insulin to stimulate mobilization of a pool of insulin-responsive vesicles to the plasma membrane. HCV-replicating cells demonstrated increases in cellular lipids with insulin resistance at the level of the insulin receptor, increased insulin receptor substrate 1 (Ser-312), and decreased Akt (Ser-473) activation in response to insulin. C/EBPβ-RNAi normalized lipogenic genes sterol regulatory element-binding protein-1c, peroxisome proliferator-activated receptor γ, and liver X receptor α but was unable to reduce accumulation of triglycerides in Huh.8 cells or reverse the increase in ApoB expression, suggesting a role for increased lipid retention in steatotic hepatocytes. Collectively, these data reveal an important role of NS5A, C/EBPβ, and pCREB in promoting HCV-induced gluconeogenic gene expression and suggest that increased C/EBPβ and NS5A may be essential components leading to increased gluconeogenesis associated with HCV infection.

Liver X receptor α-mediated regulation of lipogenesis by core and NS5A proteins contributes to HCV-induced liver steatosis and HCV replication

Molecular mechanisms contributing to hepatitis C virus (HCV)-associated steatosis are not well established, although HCV gene expression has been shown to alter host cell cholesterol/lipid metabolism. As liver X receptors (LXRs) play a role as key modulators of metabolism signaling in the development of steatosis, we aimed to investigate in an HCV in vitro model the effect of HCV NS5A protein, core protein, and viral replication on the intracellular lipid accumulation and the LXRα-regulated expression of lipogenic genes. The effects of LXRα siRNA or agonist GW3965 treatment on lipogenesis and HCV replication capacity in our HCV replicon system were also examined. NS5A- and core-expressing cells and replicon-containing cells exhibited an increase of lipid accumulation by inducing the gene expression and the transcriptional activity of LXRα, and leading to an increased expression of its lipogenic target genes sterol regulatory element binding protein-1c, peroxisome proliferator-activated receptor-γ, and fatty acid synthase. Transcriptional induction by NS5A protein, core protein, and viral replication occurred via LXR response element activation in the lipogenic gene promoter. No physical association between HCV proteins and LXRα was observed, whereas NS5A and core proteins indirectly upregulated LXRα through the phosphatidylinositol 3-kinase pathway. Finally, it was found that LXRα knockdown or agonist-mediated LXRα induction directly regulated HCV-induced lipogenesis and HCV replication efficiency in replicon-containing cells. Combined, our data suggest that LXRα-mediated regulation of lipogenesis by core and NS5A proteins may contribute to HCV-induced liver steatosis and to the efficient replication of HCV.

Do hepatitis B virus and hepatitis C virus co-infections increase hepatocellular carcinoma occurrence through synergistically modulating lipogenic gene expression?

Hepatitis B virus (HBV) and hepatitis C virus (HCV) infections cause a wide range of liver diseases including hepatocellular carcinoma (HCC). Because of the similar modes of transmission, HBV HCV co-infections are found in approximately 7-20 million people globally. Compared with HBV or HCV mono-infections, co-infections are associated with more severe liver diseases and higher risk of HCC. Abnormal lipid biosynthesis and metabolism has been increasingly recognized as a cause for cancer. While HBV infection does not seem to significantly increase the risk of developing hepatic steatosis, steatosis is a prominent feature of chronic hepatitis C (CHC). In addition, steatosis in HBV or HCV mono-infections is a significant and independent risk factor for HCC. However, whether and how HBV HCV co-infections synergistically increase the risk of HCC development through modulating lipid metabolism is not well understood. Possible mechanisms by which steatosis causes HCC include: activation of sterol regulatory element-binding protein-mediated lipogenesis through the PI3K-Akt pathway, abnormal activation of peroxisome proliferator-activated receptors and endoplasmic reticulum stress. Here, we review the potential mechanisms by which HBV HCV co-infections may increase HCC risk through modulation of lipogenic gene expression. We begin with reviewing the impact of HBV and HCV on host lipogenic gene expression and carcinogenesis. We then discuss the potential mechanisms by which HBV and HCV can increase carcinogenesis through synergistically activating lipid biosynthesis and metabolism. We end by sharing our thoughts on future research directions in this emerging paradigm with an ultimate goal of developing effective therapeutics.

SKI-1/S1P inhibition: a promising surrogate to statins to block hepatitis C virus replication

Hepatitis C virus (HCV) is often associated with steatosis, cirrhosis and hepatocellular carcinoma (HCC). Statins (HMG-CoAR inhibitors) have been shown to exert an antiviral effect in vitro, principally on replicon harboring cells, but the effect of their use alone in vivo remains controversial. In clinical trials, when used in combination with the standards of care (SOC), they led to an increased proportion of sustained virological responder (SVR). Here we investigated the implication of SKI-1/S1P, a master lipogenic pathways regulator upstream of HMG-CoAR, on different steps of HCV life cycle. We compared the HCV antiviral effect of the most potent SKI-1/S1P small molecule inhibitor (PF-429242) with a set of two statins on different steps of the viral life cycle, and showed that SKI-1/S1P inhibitor blocked HCVcc (strain JFH-1) RNA replication (EC(50)= 5.8 μM) more efficiently than statins. Moreover, we showed that PF-429242 could reduce lipid droplets accumulation in Huh7 cells. Interestingly, PF-429242 dramatically reduced infectious particles production (EC(90)= 4.8 μM). Such inhibition could not be achieved with statins. SKI-1/S1P activity is thus essential for viral production and its inhibition should be considered for antiviral drug development.

Recent progress in histochemistry and cell biology

Studies published in Histochemistry and Cell Biology in the year 2011 represent once more a manifest of established and newly sophisticated techniques being exploited to put tissue- and cell type-specific molecules into a functional context. The review is therefore the Histochemistry and Cell Biology's yearly intention to provide interested readers appropriate summaries of investigations touching the areas of tissue biology, developmental biology, the biology of the immune system, stem cell research, the biology of subcellular compartments, in order to put the message of such studies into natural scientific-/human- and also pathological-relevant correlations.

Treatment of patients with genotype 3 chronic hepatitis C--current and future therapies

Genotype 3 is a common type of HCV infection, and standard therapy using pegylated interferon (PEG-IFN) and ribavirin (RBV) is quite effective in these patients. While a short course of 16 weeks may result in comparable end of therapy responses, relapse rates are often high. A 24-week course is therefore preferable, and is expected to result in sustained virological response (SVR) rates of more than 70%. The 24-week course is especially recommended in the presence of steatosis (often associated with Genotype 3 infection), fibrosis stage two or more, high BMI and high viral load. In patients who do not achieve a rapid viral response (RVR) with combination therapy, an extended course up to 48 weeks should be considered. While not as definite as for genotype 1 patients, the presence of the CC variant of IL28b could help in the initial prognosis and the need for additional treatment, if an RVR is not achieved. The role of directly acting antiviral agents (DAA) has not been fully evaluated in treatment naïve, non-responders and relapsers in genotype 3 patients. Initial results with the cyclophilin inhibitor Debio-025 are quite encouraging. There is an urgent need for large clinical trials using DAA and host modulators in patients with G3 infection.

From virus entry to release: the diverse functions of PI3K during RNA virus infections

RNA viruses are the causative agents of severe diseases in vertebrates. Upon viral infection, various intracellular signaling pathways are induced within the infected cells. While most of the different cellular signaling responses are initiated as antiviral defense mechanisms to counteract invading pathogens, they may also be exploited by viruses to support their replication. Recently, PI3K has been added to the growing list of signaling factors and pathways that are activated upon viral infections and regulate the replication process. Here, the current knowledge on RNA virus-induced PI3K-regulated signaling processes and how the pathogens take advantage of these activities within the infected cells is summarized.

HCV genotype 3 is associated with a higher hepatocellular carcinoma incidence in patients with ongoing viral C cirrhosis

Liver steatosis is a main histopathological feature of Hepatitis C (HCV) infection because of genotype 3. Steatosis and/or mechanisms underlying steatogenesis can contribute to hepatocarcinogenesis. The aim of this retrospective study was to assess the impact of infection with HCV genotype 3 on hepatocellular carcinoma (HCC) occurrence in patients with ongoing HCV cirrhosis. Three hundred and fifty-three consecutive patients (193 men, mean age 58 ± 13 years), with histologically proven HCV cirrhosis and persistent viral replication prospectively followed and screened for HCC between 1994 and 2007. Log-rank test and Cox model were used to compare the actuarial incidence of HCC between genotype subgroups. The patients infected with a genotype 3 (n = 25) as compared with those infected with other genotypes (n = 328) had a lower prothrombin activity [78 (interquartile range 60-85) vs 84 (71-195) %, P = 0.03] and higher rate of alcohol abuse (48%vs 29%, P = 0.046). During a median follow-up of 5.54 years [2.9-8.6], 11/25 patients (44%) and 87/328 patients (26%) with a genotype 3 and non-3 genotype, respectively, develop a HCC. HCC incidences were significantly different among the genotype subgroups (P = 0.001). The 5-year occurrence rate of HCC was 34% (95% CI, 1.3-6.3) and 17% (95% CI, 5.7-9.2) in genotype 3 and non-3 genotype groups, respectively (P = 0.002). In multivariate analysis, infection with a genotype 3 was independently associated with an increased risk of HCC occurrence [hazard ratio 3.54 (95% CI, 1.84-6.81), P = 0.0002], even after adjustment for prothrombin activity and alcohol abuse [3.58 (1.80-7.13); P = 0.003]. For patients with HCV cirrhosis and ongoing infection, infection with genotype 3 is independently associated with an increased risk of HCC development.

Down-regulation of phosphatase and tensin homolog by hepatitis C virus core 3a in hepatocytes triggers the formation of large lipid droplets

Hepatitis C virus (HCV) perturbs the host's lipid metabolism and often results in hepatic steatosis. In nonalcoholic fatty liver disease, the intrahepatic down-regulation of phosphatase and tensin homolog deleted on chromosome 10 (PTEN) is a critical mechanism leading to steatosis and its progression toward fibrosis and hepatocellular carcinoma. However, whether an HCV infection triggers the formation of large lipid droplets through PTEN-dependent mechanisms is unknown. We assessed PTEN expression in the livers of patients infected with HCV genotype 1 or 3 with or without steatosis. The role of PTEN in the HCV-induced biogenesis of lipid droplets was further investigated in vitro with hepatoma cells transduced with the HCV core protein of genotype 1b or 3a. Our data indicate that PTEN expression was down-regulated at the posttranscriptional level in steatotic patients infected with genotype 3a. Similarly, the in vitro expression of the HCV genotype 3a core protein (but not 1b), typically leading to the appearance of large lipid droplets, down-regulated PTEN expression by a mechanism involving a microRNA-dependent blockade of PTEN messenger RNA translation. PTEN down-regulation promoted in turn a reduction of insulin receptor substrate 1 (IRS1) expression. Interestingly, either PTEN or IRS1 overexpression prevented the development of large lipid droplets, and this indicates that the down-regulation of both PTEN and IRS1 is required to affect the biogenesis of lipid droplets. However, IRS1 knockdown per se did not alter the morphology of lipid droplets, and this suggests that other PTEN-dependent mechanisms are involved in this process.

CONCLUSION

The down-regulation of PTEN and IRS1 is a critical event leading to the HCV genotype 3a-induced formation of large lipid droplets in hepatocytes.